Abstract

We report the collaborative experimental and theoretical study of the time-resolved recombination dynamics of photodissociated clusters. Excitation of the bare anionic chromophore to the dissociative state yields only and Br products. Interestingly, however, the addition of a few solvent molecules promotes recombination of the dissociating chromophore on the ground state, which correlates asymptotically with and I products. This process is studied experimentally using time-resolved, pump-probe techniques and theoretically via nonadiabaticmolecular dynamics simulations. In sharp contrast to previous studies where more kinetic energy was released to the photofragments, the observed recombination times increase from picoseconds to nanoseconds with increasing cluster size up to . The recombination times then drop dramatically back to picoseconds for cluster sizes . This trend, seen both in experiment and theory, is explained by the presence of a solvent-induced well on the state, the depth of which directly corresponds to the asymmetry of the solvation about the chromophore. The results seen for both the branching ratios and recombination times from experiment and theory show good qualitative agreement.

Received 23 September 2008Accepted 04 November 2008Published online 09 December 2008

Acknowledgments:

We gratefully acknowledge support from the National Science Foundation, Awards CHE0809391 and PHY 0551010, and the Air Force Office of Scientific Research, Award FA9550-06-1-0066. We also thank Dr. Joseph Fowler, Dr. Nikki Delaney, Dr. James Faeder, and Dr. Paul Maslen for their discussions on all aspects of this work.